* Astronomy

NASA Scientists to Discuss Search for Habitable Planets, Signs of Life off Earth

NASA scientists from across the agency will present their latest findings and perspectives on topics ranging from the origins and evolution of life on Earth to the search for habitable environments and life in our solar system and beyond during the 2017 Astrobiology Science Conference, April 24-28 in Mesa, Arizona
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Title: On the visible size and geometry of aggressively expanding civilizations at cosmological distances
Author: S. Jay Olson

If a subset of advanced civilizations in the universe choose to rapidly expand into unoccupied space, these civilizations would have the opportunity to grow to a cosmological scale over the course of billions of years. If such life also makes observable changes to the galaxies they inhabit, then it is possible that vast domains of life-saturated galaxies could be visible from the Earth. Here, we describe the shape and angular size of these domains as viewed from the Earth, and calculate median visible sizes for a variety of scenarios. We also calculate the total fraction of the sky that should be covered by at least one domain. In each of the 27 scenarios we examine, the median angular size of the nearest domain is within an order of magnitude of a percent of the whole celestial sphere. Observing such a domain would likely require an analysis of galaxies on the order of a Gly from the Earth.

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Title: The Age Distribution of Potential Intelligent Life in the Milky Way
Author: Daniel Legassick

We investigated the habitability of the Milky Way, making use of recent observational analysis on the prevalence of Earth-sized planets, in order to estimate where and when potentially habitable star systems may have formed over the course of the Galaxy's history. We were then able to estimate the age distribution of potential intelligent life in our Galaxy using our own evolution and the age of the Sun as a proxy. To do this we created a galactic chemical evolution model and applied the following habitability constraints to the Sun-like (G-type) stars formed in our model: an environment free from life-extinguishing supernovae, a high enough metallicity for Earth-sized planet formation and sufficient time for the evolution of complex life. We determined a galactic habitable zone as the region containing all the potentially habitable star systems in our model. Our galactic habitable zone contains stars formed between 11 and 3.8 billion years ago at radial distances of between 7 and 14 kiloparsecs. We found that most potentially habitable star systems are much older than the Sun and located farther from the galactic centre. By comparing the ages of these systems we estimated that 77% of potentially habitable star systems are on average 3.13 billion years older than the Sun. This suggests that any intelligent life in the Galaxy is likely to be incredibly more advanced than we are assuming that they have evolved under similar timescales than we have. Implications and limitations of our study are discussed.

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Colourful life-form catalogue helps discern if we're alone

While looking for life on planets beyond our own solar system, a group of international scientists has created a colourful catalogue containing reflection signatures of Earth life forms that might be found on planet surfaces throughout the cosmic hinterlands. The new database and research, published in the March 16 Proceedings of the National Academy of Sciences (PNAS), gives humans a better chance to learn if we are not alone.
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